Veterans aged 65 years old or older are eligible to use both the Veterans Health Administration (VHA) system, and the private health care delivery system via Medicare. Such "dual" system use can have both positive and negative effects. We hypothesize that dual use among older male veterans increases their risk of being hospitalized for ambulatory care sensitive conditions (ACSCs), and increases their risk of mortality. We examine this hypothesis among older male veterans in the Survey of Assets and Health Dynamics Among the Oldest Old (AHEAD), which included 2,911 men aged 70 years old or older at baseline (1993). 1,574 (54%) of the AHEAD men are veterans, and 281 (17.9%) reported having a service-related disability. We will link the AHEAD survey data to Medicare claims and the National Death Index, and we will geocode data on health care market structure. Because VHA claims data are not available, we will indirectly measure dual use based on the discrepancy between self-report and Medicare claims through a 3-step process: (1) identify discordance between self-reported use and Medicare claims by generating binary inpatient and outpatient reporting discrepancy markers; (2) create propensity scores for the likelihood of discordance on each of the markers in Step 1 using multiple logistic regression and all appropriate baseline covariates including the veterans' status marker; and, (3) use the propensity scores obtained in Step 2 and the veterans' status marker to (a) first additively model the risk of ACSCs and mortality after baseline, then (b) add a marker for the multiplicative interaction between the veterans' status marker and the propensity scores to tap their synergistic effect, and finally (c) adjust for potential confounders in an attempt to decompose the effect observed in Step 3b. We will use proportional hazards models and our focus is on the multiplicative interaction between the veterans' status marker and the propensity score. Because non-veterans are coded zero on the veterans' status marker, significant and positive parameter estimates for this multiplicative interaction term will be prima facie evidence supporting our hypothesis. At that point we will petition AHEAD, VHA, and CMS for permission to link VHA claims to the existing AHEAD comprehensive data files, and then propose a follow-on NIH R01 study to provide a more definitive and direct examination of our hypothesis about the adverse effect of dual use on health care outcomes using both Medicare and VHA claims data. [unreadable] [unreadable] [unreadable] [unreadable]